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Measles were largely eradicated in America by the turn of the century; the U.S. Centers for Disease Control and Prevention (CDC) verified in 2000 that the disease had been eliminated within the borders of the country. However, in recent years the respiratory disease has reappeared, albeit sporadically.

In 2011 (the last year for which there is complete data), the CDC reported a sharp increase in cases of measles per year to 222 diagnoses, mostly attributable to illnesses developed during overseas travel to and from Europe and Asia. Nearly 40 percent of those sickened had contracted measles from foreign countries, spreading the disease to others in 17 separate outbreaks. Across the Atlantic, British health officials noted an uptick from a few dozen cases to more than 2,000 last year and another 1,200 by May.

The vaccine for the measles has been widely available (and affordable) in the U.S. for years. Administered as the measles, mumps, and rubella (MMR) vaccine, the vaccine is manufactured by U.S.-based Merck and was approved by the U.S. Food and Drug Administration in 1971.

So why has the measles returned in the U.S.? The answer leads to one of the most controversial subject matters in recent public health policy history.

While nearly all the scientific evidence shows the MMR vaccine to be safe and effective for children, a small minority of studies showing a link between the development of autism spectrum disorder and the MMR vaccine has fuelled pockets of resistance to childhood immunizations for the past 15 years. And while all public health authorities in the U.S. and the U.K. have stated unequivocally that the MMR vaccine is safe, a libertarian distrust of public health officials in the two countries has led to shifting personal health practices.

The result? In recent years, some parents have decided that their children would not be vaccinated against measles — fearing their children would develop autism.

Andrew Wakefield And The Supposed MMR-Autism Connection

Resistance in the U.S. and U.K. to childhood immunizations such as MMR vaccine began 15 years ago when the Lancet published a study in 1998 showing an association with the development of autism spectrum disorder. By 2004, the British medical journal had retracted the paper from embattled researcher Andrew Wakefield as 10 of his 12 co-authors withdrew support for the study amid exposure by British journalists of financial conflicts of interest. By 2010, Wakefield had been stripped of his medical license.

A number of subsequent studies failed to demonstrate any association between the vaccine and autism — with a couple of exceptions.

In 2002, investigators at Utah State University published a study showing evidence of an abnormal reaction to the vaccine in children with autism, providing some encouragement to parents who have refused to vaccinate their children with the typical three-shot regimen.

In comparing 125 children with autism spectrum disorder with 92 others, Vijendra Singh and his colleagues found antibodies demonstrating an unusual reaction to the vaccine, with 90 percent of those children testing positive for antibodies suspected to be linked to the condition. Such antibodies target myelin in the brain, which serves as an insulator allowing nerve fibers to develop properly.

The study was widely reported throughout the U.K. and U.S. press, and continues to be used by critics of the MMR vaccine. On the other hand, supporters of the MMR vaccine criticized the study on methodological grounds, asserting that no causal link between the vaccine and autism had been proven. Additionally, the American Academy of Pediatrics, the CDC, and other supporters of the MMR vaccine cite a great number of scientific studies supporting the safety of the vaccine for children.

Most Studies Show No Link Between MMR and Autism

In 2001, the Journal of Pediatrics published a study that found no evidence to support the idea of an “MMR-induced autism,” which, according to the study, supports “the recent accumulation of large-scale epidemiologic studies that all failed to support an association between MMR and autism at population level.” A 2002 study published in BMJ that looked at people with autism born between 1979 and 1998 backed up this conclusion.

In 2004, the Institute of Medicine sent 15 medical experts to Congress to vouch for the safety of the vaccine, after publishing a report the preceding year finding that “the evidence favors rejection of a causal relationship at the population level between MMR vaccine and autistic spectrum disorders.”

Also in 2004, an Annals of Pharmacotherapy paper performed a meta-analysis of the literature between 1966 and 2003 to attempt to evaluate the proposed connection of MMR and autism development. The study concluded that “based upon the current literature, it appears that there is no relationship between MMR vaccination and the development of autism.

A large-scale Japanese study published in 2005 in the Journal of Child Psychology and Psychiatry looked at the incidence of autism spectrum disorder in about 300,000 children born in Yokohama between 1988 and 1996. Interestingly, not a single MMR vaccine was administered in the city in 1993 or after, so the study offered a unique set of data to investigate. The result: there was actually a notable increase in autism for the birth cohort of 1993-1996 vs. 1988-1993.

In 2006, the Journal of Pediatrics published a major Canadian study that found no connection between pervasive developmental disorders (autism is the most characteristic condition in this category of disorders, also sometimes referred to as PDD) and the MMR vaccine. The study looked at 27,749 children born between 1987 and 1998. The researchers discovered that while PDD was higher in this birth cohort than in previous years, it had nothing to do with exposure to the MMR vaccine. The authors concluded that “MMR vaccination is most unlikely to be a main cause of ASD [and] it cannot explain the rise over time in the incidence of ASD.”

A smaller 2008 PLOS One Study looked at 25 children with autism and 13 children without the developmental disorder and found “strong evidence” against any connection between MMR exposure and autism.

In March of 2010, the Journal of Pediatricspublished a study funded by the CDC finding no link between MMR vaccinations and the development of autism. The researchers analyzed data from 256 children with autism spectrum disorder and 752 other children who were matched for age, sex, and other factors, ensuring the integrity of the study by evaluating autism diagnoses with in-person examinations. They concluded that “increasing exposure to antibody-stimulating proteins and polysaccharides in vaccines during the ﬁrst 2 years of life was not related to the risk of developing an ASD.

Why People Still Resist The MMR Vaccine

Not convinced by the repudiation of Wakefield and a preponderance of scientific evidence showing no link between MMR vaccine and autism spectrum disorder, some parents in the U.S. — and elsewhere — continue to invoke the medical, philosophical, and religious exemption from public health law requiring such childhood immunizations.

Overall, the CDC reported in 2011 that exemption rates nationwide ranged from less than one percent to 6.2 percent for all vaccines, with pockets of resistance running higher in certain counties in California and the libertarian-strong Pacific Northwest. Approximately one-third of parents surveyed by Institute of Medicine (IoM) in 2003, for example, expressed concerns about the safety of childhood vaccines including the MMR regimen, while 10 percent of parents refused or delayed required immunizations for their children at the time.

Vaccine opponents say public health officials overemphasize the disgrace of Wakefield and either ignore or discount, on methodological grounds, any other study suggesting a link, now or then, between MMR vaccine and autism spectrum disorder. They tend to shuck responsibility for “herd immunity” for fear of even rare repercussions, real or imagined.

Thimerasol and Autism

Contrary to what many believe, the MMR vaccine does not contain — and, in fact, has never contained — thimerosal.

The confusion around thimerasol has to do primarily with an issue of adjacency; many studies have attempted to look at BOTH thimerasol-containing vaccines and the MMR vaccine at the same time, with regard to their potential connections to autism.

An American study found a "close correlation between mercury doses from thimerosal-containing childhood vaccines and the prevalence of autism from the late 1980s through the mid-1990s.”

Publishing in Medical Science Monitor, the U.S. researchers found “biological plausibility and epidemiological evidence showing a direct relationship between increasing doses of mercury from thimerosal-containing vaccines and neurodevelopmental disorders, and measles-containing vaccines and serious neurological disorders.” They recommended that thimerosal be removed from all vaccines, including influenza vaccine.

However, federal regulators today discount the 2004 study. “Thimerosal is a mercury-containing preservative used in some vaccines and other products since the 1930s,” the CDC states on its website. “There is no convincing evidence of harm caused by the low doses of thimerosal in vaccines, except for minor reactions like redness and swelling at the injection site.”

A number of studies have proven that thimerosal is safe. Most influential of this is a 2003 study published in the American Journal of Preventive Medicine that shows an increase in autism diagnoses in Sweden and Denmark even after those countries discontinued the use of thimerosal in vaccines.

In response to worldwide reports of a growing incidence of autism spectrum disorder from the mid-1980s to the turn of the century, American researchers analyzed population-based data from the U.S., comparing vaccination coverage with diagnoses of autism, and autism-like disorders, in California and in Sweden and Denmark.

During that time, the incidence of autism rose in all three countries, despite the cessation of thimerosal use in vaccines in the two Scandinavian nations. They concluded, “the body of existing data, including the ecologic data presented herein, is not consistent with the hypothesis that increased exposure to thimerosal-containing vaccines is responsible for the apparent increase in the rates of autism in young children being observed worldwide.”

A newer study conducted by CDC concluded in September of 2010 that prenatal and infant exposure to vaccines and immunoglobulins containing thimerosal “does not increase the risk for autism spectrum disorder.”

In that particular study, CDC investigators compared 256 children with autism spectrum disorder with 752 children with no neurodevelopmental problems, assessing whether ethylmercury from thimerosal had posed a threat. But no link was found, as both groups had been exposed to similar levels of the preservative.

Despite this evidence the CDC — with support from the U.S. Public Health Services, the American Academy of Pediatrics, the American Academy of Family Physicians, and vaccine manufacturers such as Merck — decided in 1999 to reduce or eliminate thimerosal in vaccines. Since then, all childhood vaccines except for multi-dose formulations for influenza have been made without thimerosal. Maintaining the safety of the mercury based preservative, the CDC says mass demand for seasonal influenza vaccine requires some the supply to be delivered in multi-dose vials, which must be protected from bacterial and fungal infection.

Autism In the 21st Century

As to why diagnoses of autism spectrum disorder have risen worldwide since the mid-1980s, medical experts have no definitive answer. Today, the CDC says one in 54 boys in America fall within the autistic range, with the condition nearly five times as common in boys as in girls. It’s one of the fastest-growing developmental disabilities, and is becoming a major public health concern. It remains one of the most controversial subjects in health and medical science.